Table 4 Subgroup analysis for the risk of mortality according to the baseline GFR.

From: Low serum total CO2 and its association with mortality in patients being followed up in the nephrology outpatients clinic

Subgroup

Model

Cox regression analysis

Instrumental variable analysis

HR

95% CI

P

HR

95% CI

P

GFR < 30 (n = 4215)

1

0.989

(0.976, 1.002)

0.089

0.823

(0.656, 1.031)

0.090

2

0.988

(0.975, 1.001)

0.072

0.801

(0.625, 1.027)

0.081

3

0.986

(0.973, 0.999)

0.036

0.778

(0.607, 0.998)

0.048

4

0.981

(0.968, 0.994)

0.004

0.760

(0598, 0.966)

0.025

5

0.996

(0.983, 1.009)

0.537

0.759

(0.606, 0.950)

0.016

6

0.991

(0.977, 1.004)

0.173

0.746

(0.601, 0.926)

0.008

7

0.993

(0.980, 1.007)

0.329

0.720

(0.582, 0.890)

0.002

30 ≤ GFR < 60 (n = 9446)

1

0.924

(0.913, 0.935)

 < 0.001

0.769

(0.682, 0.867)

 < 0.001

2

0.926

(0.915, 0.937)

 < 0.001

0.759

(0.672, 0.857)

 < 0.001

3

0.918

(0.907, 0.929)

 < 0.001

0.688

(0.609, 0.776)

 < 0.001

4

0.915

(0.904, 0.927)

 < 0.001

0.687

(0.609, 0.776)

 < 0.001

5

0.925

(0.914, 0.937)

 < 0.001

0.662

(0.571, 0.766)

 < 0.001

6

0.923

(0.911, 0.935)

 < 0.001

0.667

(0.577, 0.772)

 < 0.001

7

0.926

(0.914, 0.938)

 < 0.001

0.615

(0.531, 0.711)

 < 0.001

GFR ≥ 60 (n = 28,570)

1

0.924

(0.912, 0.936)

 < 0.001

0.412

(0.221, 0.770)

0.005

2

0.939

(0.927, 0.951)

 < 0.001

0.390

(0.217, 0.700)

0.002

3

0.934

(0.922, 0.946)

 < 0.001

0.305

(0.170, 0.547)

 < 0.001

4

0.937

(0.925, 0.949)

 < 0.001

0.326

(0.185, 0.573)

 < 0.001

5

0.936

(0.924, 0.948)

 < 0.001

0.273

(0.136, 0.549)

 < 0.001

6

0.939

(0.927, 0.952)

 < 0.001

0.296

(0.151, 0.580)

 < 0.001

7

0.942

(0.930, 0.954)

 < 0.001

0.280

(0.145, 0.540)

 < 0.001

  1. Model 1: TCO2 only.
  2. Model 2: Model 1 + history of hypertension and diabetes.
  3. Model 3: Model 2 + sex and age.
  4. Model 4: Model 3 + usage of sodium bicarbonate.
  5. Model 5: Model 3 + baseline kidney function as MDRD-GFR.
  6. Model 6: Model 5 + usage of sodium bicarbonate.
  7. Model 7: Model 6 + RAAS blockades + Diuretics group.
  8. CI confidence interval, GFR glomerular filtration rate, HR hazard ratio, TCO2 total CO2.
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